1. XFEL Project Overview R. Brinkmann, DESY S2E Workshop, Zeuthen, Aug. 18, 2003

2. TESLA TDR, March 2001: integrated XFEL

3. Considerations leading to XFEL TDR-update, autumn 2002 Avoid strong “coupling” of XFEL and LC parts of TESLA project during construction, commissioning and operation stages (and: approval) Gain flexibility in operation parameter space  XFEL driver linac in separate tunnel Limitation of additional cost:  Reduce linac length & energy to ~1.5km, 20 GeV  Difference in accelerator cost: (sep. linac – TDR2001) = 196 Mio. €  Reduce # of photon beam lines 10  5, # of experiments 30  10

4. Comparison of parameters (1Å, fixed-gap undulator)

5. Injector: = TTF-II

6. Simulations (60MV/m cathode field) indicate  < 1 mm*mrad possible Including BCs (CSR!), phase space structure non-trivial  start- to-end simulations Linac wakefields unlikely a serious problem Exploration of bunch parameter space (e.g. charge vs. emittance & bunch length) ?

7. 3.9km

9. Recent discussions/developments Shortening of the accelerator (Injector + linac + collimation/diagnostic etc.) tunnel to ~2km –The “trend” is that arguments towards higher beam energy become weaker – more aggressive undu’s, perhaps better beam quality (careful: we haven’t seen the 1.4 mm*mrad yet…), h.h. generation; this together with recent achievements in cav. Performance makes linac length extendibility hard to justify (cost!)cav. Performance XFEL site layout not anymore linked to LC site  explore possible DESY-near sitesDESY-near –No green light from government for an LC site near Hamburg at this point in time; process in int. community towards LC technology decision, int. funding and site decision likely to take several years –Synergy/cost saving arguments for Ellerhoop site can’t be used anymore to push the plan approval procedure through

10. Linac to be constructed in TTF-like technology: 12m modules with 8 cavities + quad package –R&D effort and investment in infrastructure necessary to develop 17m modules with superstructures not in healthy balance with potential gains for a 1.5km linac (different for 30km LC!) Limit average beam power to ~600 kW (max. 300 kW per solid state beam dump in the 1st stage with two dumps)

12. Start with reference parameter set…

13. Comment 1: energy management in case of failure requires reserve RF units in both section 1 and 2 of main linac (maintain 2.5 GeV energy at BC-III) Comment 2: lower gradient in section 1 can be advantageous in view of desirable rep. Rate flexibility (see below)

14. ...and investigate optimisation towards cost saving, operational flexibility, … More modules (6 instead of 4) per 10MW klystron Duty cycle/rep rate flexibility/limitations –Cryogenics: f rep up to 20Hz/20 GeV possible with cryo plant size of one (of six) TESLA500 plant and unchanged He distribution concept; f rep  1/energy 2 possible for lower E operation; CW at 20 GeV excluded (3 times entire TESLA500 2K capacity!) –RF system: can trade rep rate vs peak power  model calculation taking into account properties of 10MW MBK, but not other possible limitations (modulator power switch, RF drive, etc.) –Injector needs special consideration (e.g. shorter pulses in RF gun at higher f rep, laser limitations?)

15. Remark: av. Beam power is maximum possible - because of beam dump (solid absorber option) we wanted to limit P av  600kW Max rep rate and beam power, four vs. six modules/klystron

16. What can we gain from variable Q ext ? Example (6 modules): Keep I b = 5 mA const., scale Q ext  E acc Attractive option: shorter pulses/higher f rep (RF gun!)

17. Options, not part of 1 st stage Adding more beam lines: in principle straight forward, need to take additional beam distribution requirements into account (facilitate civil construction, leave space for kicker magnets etc.) Site dependent: do not exclude using the linac as injector for PETRA and/or HERA Do not exclude the far future possibility of operating in CW/ERL mode –Can’t work out a full detailed design for this, but have to avoid “stupid mistakes” (like non (2n+1)/2 cavity and module spacing or a fixed Q_ext which can’t be changed without taking the entire linac apart) –Possible at any site, but has site-dependent aspects Challenge is to avoid too much entropy in the project preparation process without missing important future opportunities!

18. XFEL – Linear Collider Synergies Working towards getting ready for start of construction of 20 GeV s.c. linac in ~2 years from now is a big step forward for making TESLA technology available for large-scale projects The issues in common for developing the 500-800 GeV LC s.c. linac and getting ready for constructing the XFEL linac (by far) outweigh those issues which may be different and may require potential priority conflict discussions There is also overlap between LC and XFEL for a number of other design issues and sub-systems (e.g. failure handling/operational reliability, beam size and profile monitoring, fast orbit feedback, LLRF…)

19. Example 1: Tunnel Layout E.g.: Electronics in tunnel/radiation environment (  test in DESY-LINAC-II) Handling of RF and cavity failures Stray fields? Supports and alignment

20. Example 2: fast kicker systems Damping ring: re-distribute the train of bunches in time (compress/de-compress at injection/ejection) XFEL user beam lines: distribute bunches within a train to different beam lines (possibly extraction points at different energies, etc…) Technology for both applications may also be similar to fast orbit feedback requirements

21. XFEL Project Group at DESY – 1 st meeting Aug. 6 group leaders: R. Brinkmann (mainly accelerator), A. Schwarz (mainly user facility) Structure the work necessary to prepare for start of project construction in ~ two years  total of 38 work packages (reasonable break down of work to start with – not necessarily 100% static, may want to re-define in some cases later) WPs cover all categories for complete project definition: –Overall design & parameters, beam physics –Major technical components –Sub-systems –Other issues like “site and civil construction”, “safety”, etc. Try to (ideally) have one DESY representative for each WP (WP leader at DESY) To avoid mis-understanding: this does not mean to imply that DESY wants to take over all tasks! Leadership and/or participation from other labs is already present, especially for s.c. linac technology  participation from outside will grow in the future and have to be integrated in the Project Group http://xfel.desy.de